For example, video display devices, which are portable electronic devices such as personal computers, are capable of operating even without connection with a commercially available power source. In the field of television receivers configured to receive television broadcasting, the types that operate using mainly a battery have been commercially practical.
In recent years, electricity saving has been a big topic, especially with the power supplied from power plants of electricity supply companies. When the total amount of power consumption of a jurisdictional area becomes greater than the amount of power supplied from the power plants, a blackout might occur and cause serious damage to factories, hospitals, and the like.